Hydrogen sulfide (H2S) is a highly toxic and corrosive gas that is a common contaminant of raw natural gas, groundwater and petroleum refinery operations. Many strategies have been developed to remove hydrogen sulfide from natural gas and sour gas streams generated in the oil and gas industry. Sodium hydroxide (NaOH) is an effective scrubbing agent for hydrogen sulfide removal from mixed gas streams, with a strongly favorable equilibrium constant and rapid kinetics. However, due to high cost of single use capture and the lack of a feasible regeneration process, NaOH is generally not considered to be economically viable for large scale scrubbing.
In the oil and gas industry, amine scrubbers are typically used to remove H2S from mixed gas streams. During subsequent scrubber regeneration, this H2S is then released from the amine scrubbing solution as a concentrated gas stream and further processed into sulfur by the Claus process. As an alternative to amine scrubber technology, aqueous sodium hydroxide solutions can be used to capture H2S from mixed gas streams, via the spontaneous reaction of H2S(g) with NaOH(aq) to form Na2S(aq) or NaHS(aq). A significant economic challenge in using sodium hydroxide to scrub hydrogen sulfide gas is the lack of a reliable, low cost method to regenerate the hydroxide capture reagent (i.e. to convert the Na2S(aq) or NaHS(aq) back into NaOH(aq). The amount of hydrogen sulfide processed annually far exceeds the market need for the sodium sulfide byproducts and therefore results in a linear process stream that generates significant unstable and potentially toxic chemical wastes. Furthermore, conventional production of sodium hydroxide via the chloralkali process is both costly and environmentally challenging due to co-production of toxic chlorine gas and substantial carbon dioxide emissions.